The invention relates to an assembly which is comprised of a carrier and a thin film disposed on the carrier and formed from a superconductor, whereby the thin film is provided with a multiplicity of holes through the thin film with a radius in the range of 50 to 200xc2x0 nm.
In Solid State Commun. 91, 331 (1994), Metlushko, V. V. et al describe a thin film which is comprised of a conventional type II superconductor and which is penetrated with a periodic hole grid pattern. The flux tubes which develop in the superconductive film at a sufficiently large magnetic field organize themselves in the form of a grid (Abrikosov Grid). Based upon a measurement of the direct current conductivity as a function of the strength of an external magnetic field, that article provides information as to an interchange between the Abrikosov Grid and the superimposed artificial hole grid.
In addition, for many years high temperature superconductors (HTSC) have been known. As distinct from conventional superconductors, HTSCs can operate even at the temperature of liquid nitrogen (77K) so that the cost of cooling can be drastically reduced. HTSCs, however, have the drawback that in the superconductive state, they have a high dissipation by comparison with conventional type II superconductors.
In the high frequency field, especially in the microwave range (300 MHz to 300 GHz), it is desirable to operate with walls of components such as, for example, resonators or hollow wave guides, as much as possible without losses of electrical conductivity of surface currents. For that purpose, significant HF characteristics of the corresponding components, for example, Q-factor, damping and the like, should be improved.
To reduce the ohmic losses of metal surfaces of HF components, it is already known to polish the surfaces, to plate them or to provide them with surface coatings comprised of a metal of high electrical conductivity (silver, gold).
It is also known, in addition, to improve the electrical conductivity of HF components by the use of superconductive surface layers. It is a drawback here that to maintain the conductive state of these layers, they must be cooled below their critical temperature Tc and that requires significant expenditure.
In the electrically conductive field, strip conductors are known which are comprised of a strip carrier of an electrically conductive material and an HTSC film deposited thereon.
In the measurement field, SQUIDs (SQUID: superconductive quantum interference device) are known for high sensitivity measurements of magnetic fields. With HTSC SQUIDs, it is a drawback that the measurement sensitivity is limited by a relative high low frequency noise.
The invention has as its object the provision of an assembly which can be utilized in various ways and in various fields.
A more specific object of the invention is to provide an arrangement which enables HF components to be obtained with significantly improved component characteristics and the production of superconductive strip conductors with higher current capacities and active superconducting electronic components with a low noise level.
This object is achieved, according to the invention, by providing a high temperature superconductor film on a carrier and forming the superconductor film with a multiplicity of holes with radii in the range of 50 to 2000 mm.
The invention is based upon the recognition that this can be achieved with an HTSC film with a multiplicity of holes retaining superconducting character and that this can be used technologically in a new way.
The arrangement of the invention has a number of electrical characteristics which can be used with advantage especially in the HF field, in the field of superconducting strip conductors and in the measurement field. By contrast with a known HTSC film without holes, the xe2x80x9cperforatedxe2x80x9d HTSC film according to the invention has a reduced HF surface resistance, an increased critical current amplitude for direct current and suppression of the noise in active superconductive components resulting from the tendency toward flux tube migration.
Holes in the aforementioned size range can be produced by known lithographic techniques, for example, photolithography, electrobeam lithography or x-ray lithography in combination with known etching processes. Preferably the radius of the holes is in the range of 500 to 1000 nm since holes in this size range can be produced in an especially simple way by photolithographic techniques.
The mean distance d between neighboring holes, the hole r and the thickness t of the film can be so selected as to preferably satisfy the inequality Bc1 (t/(dxe2x88x922r))0.5 greater than B, whereby Bc1 is the lower critical field of the superconductor and B is the external magnetic field. In this case, all of the flux tubes which arise from the film are anchored (pinned) at respective holes and the previously indicated advantageous characteristics (reduction of the HF surface resistance, increase of the current carrying-capacity and reduction in the noise) can be achieved with the arrangement of the invention in an especially significant way.
According to an especially preferred embodiment of the invention, the density (number per unit area) of the holes can vary from place to place over the film. This enables, for example, in regions of high external magnetic field strengths, increased temperatures or also increased current densities, an especially higher local density of holes in such challenged regions, whereby especially high HF tolerance, current carrying capacity or noise suppression can be obtained.
A further preferred embodiment of the arrangement according to the invention is characterized in that the holes are arranged in a uniform pattern, especially in the form of a hexagonal or square grid across the film. Such an arrangement of the holes is preferred since the Abrikosov grid formed from the free flux tubes has its low energy states in a hexagonal or square structure.
The arrangement according to the invention can be used in many technological fields. An advantageous field of use is in the HF field for resonators and HF conductor components for coaxial and hollow conductor (waveguide) technologies and for integrated (hybrid or monolithic) microwave circuits, for superconductor strip conductors and in the field of noise suppression with active superconductive electronic components.
A first preferred embodiment of the invention can be realized as an HF component which encompasses a hollow chamber resonator in whose interior the arrangement of the invention is provided along the walls. Hollow chamber resonators are used in microwave technology for a variety of components. In communications technology, they serve, for example, as transmitters or filters in television, radio, beacon or direction finding or mobile wireless systems. They can be used in the fields of satellite navigation and radar and serve as particle accelerators in synchrotons. Upon the integration of the arrangement of the invention in a hollow space resonator, the Q-factor of the hollow space resonator is increased. In the interior of the hollow space resonator, a dielectric medium with a dielectric constant ∈ greater than 1 can be provided. In this case, it is preferred to provide the system of the invention adjacent to the dielectric medium.
The hollow space resonator can preferably be configured as a multicavity device. In that case, the resonator can be used as a filter with improved filtering characteristics (steeper flanks) and can produce a greater band width.
A further embodiment of the invention in the HF field is characterized by providing the assembly according to the invention on an interior wall of a hollow conductor (waveguide). In this manner, a hollow conductor with reduced damping can be realized and the transmission and termination characteristics of filters, HF couplers, HF transformers, HF terminating resisters or the like can be improved.
Integrated microwave circuits (MIC) are known in the art in the form of hybrid or monolithic circuits. In hybrid integrated circuits, individual finished components (hybrid elements) are combined to a circuit, while with monolithic integrated circuits, the entire circuit is contained on a semiconductor substrate.
The HF arrangement according to the invention can preferably be used both in the field of hybrid microwave circuits and also in the field of monolithic microwave circuits. In the first case a preferred embodiment of the invention is characterized in that the carrier is formed as a component carrier and the film is structured in the characteristic shape of the HF component. In the second case, the carrier is formed as a semiconductor substrate on which an integrated circuit is formed. In both cases, the microwave capacity of the integrated circuit is increased by the provision by the film according to the invention.
According to a second preferred embodiment of the invention, the assembly of the invention is realized by providing the carrier in the form of an electrically conductive strip conductor forming an electrical conductor. This electrical conductor can be used for low loss transmission of currents or also as a current limiter (superconductor fault current limiter).
Preferably multiple layers of the film coated strip conductor carrier can be assembled to a multifilament conductor. In addition, the conductor can be configured in the form of a coil.
A third preferred embodiment of the invention can be realized by surrounding the active electronic component with the system of the invention so that the electronic component has an active component region subject to flux noise, the assembly according to the invention being provided either directly around the active component region or by forming the active component region directly in the film.
With the hole arrangement according to the invention, strong active forces (xe2x80x9cpinning forcesxe2x80x9d) are produced in the region of the active zone and are effective to anchor the flux tubes at the holes. By such anchoring, a thermally excited flux meandering or xe2x80x9cvortex hoppingxe2x80x9d is suppressed and, in this manner, the noise of the active electronic component is reduced.
An advantageous configuration of the active electronic component is characterized in that the film is in the form of a ring surrounding an inner free region and containing a Josephson contact. A superconductive ring with at least one Josephson tunnel contact is known in the field as a SQUID. The low frequency noise of a SQUID is mainly determined by fluctuations of the number of elemental flux quanta traversing the superconductive ring. To keep these fluctuations small, the free region formed by the ring is preferably surrounded on all sides by the holes.